Optical Film for Back Light Unit and Back Light Unit Including Same

ABSTRACT

An optical film for a back light unit that includes an array of light emitting diodes. The optical film includes a substrate, and a plurality of regions of spatially modulated microstructures on at least one side of the substrate. The spatially modulated microstructures have different sizes and/or shapes configured to create a gradient structure within each region. The gradient structure within each region is constructed and arranged to cause more spreading of light when positioned directly above an individual light emitting diode and less spreading of light at locations not directly above an individual light emitting diode. Within the back light unit, the gradient structure converts light beams emitted by the respective light emitting diode at different angles into a more uniform and higher on-axis luminance upon exiting the back light unit.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a non-provisional application of U.S.Provisional Patent Application Ser. No. 62/965,410, entitled “OpticalFilm for Back Light Unit and Back Light Unit Including Same” filed onJul. 13, 2020 and a non-provisional application of U.S. ProvisionalPatent Application Ser. No. 63/051,101 entitled “Optical Film for BackLight Unit and Back Light Unit Including Same” filed on Jan. 24, 2020.The entire content of U.S. Provisional Patent Application Ser. No.62/965,410 and U.S. Provisional Patent Application Ser. No. 62/965,410are herein incorporated by reference.

BACKGROUND

In the pursuit of improved image quality, liquid crystal displays (LCDs)are increasingly using a back light unit architecture 100, schematicallyillustrated in FIG. 1 , that includes a printed circuit board (PCB) 110with an array of individual short wavelength (blue) LEDs 112 bonded ontothe PCB 110. The PCB 110 may have a highly reflective surface. FIGS. 2Aand 2B illustrate a typical intensity distribution of light emitted froma single LED as a function of angle, as measured by a goniophotometer.As illustrated, the LED source approximates a Lambertian source thatemits a substantially symmetrical light distribution relative to thenadir, with the highest intensity of light at the nadir.

Returning to FIG. 1 , a series of films may be used to spread or diffusethe light emitted from the LEDs 112 so that the back light unit 100 maydeliver a more uniform light to the LCD panel (not shown) containing theliquid crystals located above the back light unit 100. As illustrated,the back light unit 100 typically includes a diffuser film 120, whichmay be, for example, a volumetric diffuser or textured surface diffuseror a micro lens array diffuser, a color conversion layer 130 that useseither quantum dots or phosphor material, for example, to convert someof the blue light emitted by the LEDs 112 to green and red light, adiffuser film 140, which may be, for example, a volumetric diffuser or atextured surface diffuser or a micro lens array diffuser, configured tospread or diffuse the light exiting the color conversion layer 130, andtwo brightness enhancing films (BEFs) 150, 160, which are often twoprism films rotated approximately 90 degrees relative to each other.There may be additional films in the back light unit 100 that are usedto improve the overall uniformity and brightness of the light beingdelivered to the LCD panel. In some back light units, white LEDs may beused without a color conversion layer.

When LEDs 112 are arranged in an array, such as the 3×3 arrayillustrated in FIG. 3 , it is desirable hide the individual LEDs 112 andpresent a bright and uniform light to the LCD panel. As noted above, oneapproach to achieving this goal is to include one or more diffusers,such as the diffuser film 120, in the back light unit 100 to diffuse,spread, or blur the beams of light emitted by the LEDs 112. FIG. 4schematically illustrates such diffusion of the light emitted by asingle LED 112, with the darker shades of grey represent a brighterlight than the lighter shades of grey. Such diffusion may also reducethe mean energy of the light.

In addition, electronic devices that include LCDs are become thinner andthinner. As a result, the back light units of such displays are alsobecoming thinner and thinner, which presents another challenge to managethe light being emitted by the LEDs 112 in an effective manner. Forexample, when the diffuser film 120 is placed over the array of LEDs112, as schematically illustrated in FIG. 5A, the individual points oflight emitted by the LEDs are diffused such that light having lessintensity from adjacent LED's 112 start to overlap to create areas oflight with higher intensity. If the thickness of the diffuser film 120is increased, which may be undesirable for thinner back light units, theindividual points of light may be spread even further and provide betteruniformity of the light, but there are still brighter and darkerregions, as schematically illustrated in FIG. 5B.

It is desirable to have a back light unit for an LCD display having anarray of blue LEDs and a thin profile, yet still deliver bright anduniform light to the LCD panel while effectively hiding the individualLEDs.

SUMMARY

The present invention is generally related to an optical film that maybe used in a back light unit of a backlit display, particularly forbacklit displays with light emitting diode (LED) light sources, as wellas a back light unit that includes the optical film.

According to an embodiment of the invention, there is provided anoptical film for a back light unit that includes an array of lightemitting diodes. The optical film includes a substrate, and a pluralityof regions of spatially modulated microstructures on at least one sideof the substrate. The spatially modulated microstructures have differentsizes and/or shapes configured to create a gradient structure withineach region. The gradient structure within each region is constructedand arranged to cause more spreading of light when positioned directlyabove an individual light emitting diode and less spreading of light atlocations not directly above an individual light emitting diode.

In an embodiment, the spatially modulated microstructures include aplurality of elongated prisms.

In an embodiment, the spatially modulated microstructures include aplurality of three-sided pyramids.

In an embodiment, the spatially modulated microstructures include aplurality of cones.

In an embodiment, a plurality of first regions is constructed andarranged to cause the first level of spreading of light, and each of theplurality of first regions includes a first plurality of parallel prismsoriented in a first direction on a first side of the substrate and asecond plurality of parallel prisms oriented in a second directionorthogonal to the first direction on a second side of the substrateopposite the first side.

In an embodiment, the first plurality of parallel prisms and the secondplurality of parallel prisms have apexes having substantially the sameangles. In an embodiment, the angles are about 90°.

In an embodiment, a plurality of second regions is constructed andarranged to cause the second level of spreading of light, and each ofthe plurality of second regions includes the first plurality of parallelprisms oriented in the first direction on the first side of thesubstrate and a third plurality of parallel prisms oriented in the firstdirection on the second side of the substrate.

In an embodiment, a plurality of third regions is constructed andarranged to cause a third level of spreading of light, the third levelbeing less than the first level and greater than the second level, andeach of the plurality of third regions includes a gradient that includesa mixture of the second plurality of prisms and the third plurality ofprisms on the second side of the substrate.

In an embodiment, a plurality of third regions surround outer perimetersof the plurality of first regions, and each of the plurality of thirdregions is constructed and arranged to cause a third level of spreadingof light, the third level being less than the first level and greaterthan the second level, and each of the plurality of third regionsincludes a gradient that includes a fourth plurality of elongated prismson the second side of the substrate continuously varying in anglerelative to the first direction and the second direction as thepositions of the fourth plurality of elongated prisms move away from thefirst regions so as to create a swirl-like pattern that surrounds thesecond plurality of elongated prisms in the first regions on the secondside of the substrate.

According to an aspect of the invention, there is provided a back lightunit that includes an array of light emitting diodes, and an opticalfilm positioned above the array of light emitting diodes. The opticalfilm includes a substrate, and a plurality of regions of spatiallymodulated microstructures on at least one side of the substrate. Each ofthe plurality of regions is positioned over a respective light emittingdiode. The spatially modulated microstructures have different sizesand/or shapes configured to create a gradient structure within eachregion. The gradient structure within each region is constructed andarranged to convert light beams emitted by the respective light emittingdiode at different angles into a more uniform and higher on-axisluminance upon exiting the back light unit.

In an embodiment, centers of the regions are positioned directly overcenters of the light emitting diodes.

In an embodiment, a plurality of first regions is constructed andarranged to cause the first level of spreading of light, and each of theplurality of first regions includes a first plurality of parallel prismsoriented in a first direction on a first side of the substrate and asecond plurality of parallel prisms oriented in a second directionorthogonal to the first direction on a second side of the substrateopposite the first side. Centers of the plurality of first regions arepositioned directly over centers of the light emitting diodes.

In an embodiment, a plurality of second regions is constructed andarranged to cause the second level of spreading of light, and each ofthe plurality of second regions includes the first plurality of parallelprisms oriented in the first direction on the first side of thesubstrate and a third plurality of parallel prisms oriented in the firstdirection on the second side of the substrate. Centers of the pluralityof second regions are positioned directly over areas between the lightemitting diodes.

These and other aspects, features, and characteristics of the presentinvention, as well as the methods of operation and functions of therelated elements of structure and the combination of parts and economiesof manufacture, will become more apparent upon consideration of thefollowing description and the appended claims with reference to theaccompanying drawings, all of which form a part of this specification.It is to be expressly understood, however, that the drawings are for thepurpose of illustration and description only and are not intended as adefinition of the limits of the invention. As used in the specificationand in the claims, the singular form of “a”, “an”, and “the” includeplural referents unless the context clearly dictates otherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

The components of the following figures are illustrated to emphasize thegeneral principles of the present disclosure and are not necessarilydrawn to scale, although at least one of the figures may be drawn toscale. Reference characters designating corresponding components arerepeated as necessary throughout the figures for the sake of consistencyand clarity.

FIG. 1 is a schematic illustration of a cross-section of a typical backlight unit for an LCD display that includes an array of LEDs;

FIG. 2A is a three-dimensional plot of a distribution of light outputfrom an LED as a function of angle, as measured by a goniophotometer;

FIG. 2B is the measured light distribution of FIG. 2A represented in twodimensions;

FIG. 3 is a schematic illustration of a top view of a portion of aprinted circuit board with the array of LEDs of the back light unit ofFIG. 1 ;

FIG. 4 is a schematic illustration of a top view of a distribution oflight output from a single LED after the light has passed through adiffuser film;

FIG. 5A is a schematic illustration of a top view of the array of LEDsof FIG. 3 after the light emitted by the LEDs has passed through thediffuser film;

FIG. 5B is a schematic illustration of the array of LEDs of FIG. 3 afterthe light emitted by the LEDs has passed through a diffuser film havinga thickness greater than the diffuser film used for FIG. 5A;

FIG. 6 is a schematic illustration of a cross-section of a back lightunit for an LCD display that includes an array of LEDs and an opticalfilm in accordance with embodiments of the invention;

FIG. 7A is a top view of an optical film in accordance with anembodiment of the invention;

FIG. 7B is a slightly more perspective view of the optical film of FIG.7A;

FIG. 8A is a luminance image of a back light unit with optical films ofthe prior art having uniform microstructures;

FIG. 8B is a luminance image of the same back light unit of FIG. 8A, butwith optical films according to embodiments of the invention;

FIG. 9A illustrates an optical performance analysis for the image ofFIG. 8A;

FIG. 9B illustrates an optical performance analysis for the image ofFIG. 8B;

FIG. 10 is an illustration of a computer-generated model of a portion ofan optical film in accordance with an embodiment of the invention;

FIG. 11 is an illustration of a computer-generated model of a portion ofan optical film in accordance with an embodiment of the invention;

FIG. 12 is an illustration of a computer-generated model of a portion ofan optical film in accordance with an embodiment of the invention;

FIG. 13 is an illustration of a computer-generated model of a portion ofan optical film in accordance with an embodiment of the invention; and

FIG. 14 is an illustration of a computer-generated model of a portion ofan optical film in accordance with an embodiment of the invention;

FIG. 15 is an illustration of a portion of an optical film in accordancewith an embodiment of the invention;

FIG. 16A is a two-dimensional plot of a distribution of light outputfrom an LED source with a 20° beam, as measured by a goniophotometer;

FIG. 16B is a two-dimensional plot of a distribution of light outputfrom the LED source having the light distribution of FIG. 16A after thelight has passed through an optical film having aligned prisms on frontand back sides of the optical film, as measured by a goniophotometer;

FIG. 16C is a two-dimensional plot of a distribution of light outputfrom the LED source having the light distribution of FIG. 16A after thelight has passed through an optical film, prisms on a front side of theoptical film oriented orthogonal to prisms on a back side of the film,as measured by a goniophotometer; and

FIG. 17 is an illustration of a portion of an optical film in accordancewith an embodiment of the invention.

DETAILED DESCRIPTION

FIG. 6 schematically illustrates a back light unit 600 according toembodiments of the present invention. As illustrated, the back lightunit 600 includes a printed circuit board (PCB) 110 on which an array ofLEDs 112 is mounted, as described above, and an optical film 610according embodiments of the invention positioned above the array ofLEDs 112 that may be used in place of or in addition to the diffuserfilm 120 of FIG. 1 . The back light unit 600 also includes the colorconversion layer 130, the diffuser film 140, and the pair of brightnessenhancement films (BEFs) 150, 160 described above with respect to FIG. 1.

The angle at which light energy from an individual LED 112 impinges onthe optical film 610 is highly position dependent. For example, asillustrated in FIG. 6 , light beams that are received by the opticalfilm 610 at locations “A”, directly above the individual LEDs 112, havea small incidence angle, typically of less than a few degrees. Lightbeams that are received by the optical film 610 at locations “B”,farther from the individual LEDs 112 and not directly above theindividual LEDs, have much larger incident angles.

The optical film 610 includes a substrate 620 and a plurality ofspatially modulated microstructures 630 on one side of a substrate 620.Although the spatially modulated microstructures 630 are illustrated asbeing on the side of the substrate 620 that faces away from the LEDs112, in other embodiments, the spatially modulated microstructures 630may be on the side of the substrate 620 that faces the LEDs 112. In anembodiment, the optical film 610 may include spatially microstructures630 on both sides of the substrate 620. In an embodiment, the opticalfilm 610 may include spatially modulated microstructures 630 on one sideof the optical film 610 and uniform microstructures or texture on theother side of the optical film 610. In an embodiment, additional opticalfilms 610 having spatially microstructures 630 in accordance withembodiments of the invention may be used in the back light unit 600. Theillustrated embodiment is not intended to be limiting in any way.

As illustrated in FIG. 6 , the optical film 610 includes a plurality ofregions 640 that each include spatially modulated microstructures 630having different sizes/shapes that are configured to create a gradientstructure within each region 640. The gradient structure within a region640 is constructed and arranged to cause more spreading of lightdirectly above an individual LED 112 (location “A”) where it is neededand less spreading of light at locations not directly above anindividual LED 112 (i.e. in between individual LED 112 s at location“B”), which converts the light beams emitted by the LED 112 at differentangles beneath the region 640 into a more uniform and higher on-axisluminance upon exiting the back light unit 600. The centers of theregions 640, and hence gradient structure, are desirably positioneddirectly over a center of a respective LED 112, as illustrated.

In the embodiment illustrated in FIG. 6 , the amplitude of themicrostructures 630 within a region 640 is spatially varied with amaximum height profile located at a lattice point in the center of theregion 640, which is located directly above the center of the LED 112.Additional parameters that can be adjusted are shapes of microstructuresas a function of position, rates of structure height change, backgroundtexture between the positions of the LEDs 112, area size of constantmicrostructures above the LEDs 112, etc. In an embodiment, thelattice-type structure may be applied to the surface of the optical film610 that faces the LEDs so that the microstructures may spread the beamsreceived from the LEDs in a spatially modulated manner as well. Theillustrated embodiment is not intended to be limiting in any way. All ofthe microstructures may be tuned to provide a smoothed distributionemanating from the top surface of the brightness enhancement film 160 ofthe back light unit 600.

FIGS. 7A and 7B are pictures of an optical film 700 according to anembodiment of the invention. The optical film 700 includes regions 710of microstructures that are constructed and arranged to provide agradient, as described above. As illustrated, the regions 710 aresubstantially circular in shape in plan view and together provide theoptical film 710 with a lattice-type structure. The center of eachregion 710 is configured to be placed directly above the center of anLED.

The performance of a back light unit with the optical film 700 over anarray of mini-LEDs was measured and compared to the performance of aprior art back light with a “standard” optical film with uniformmicrostructures (i.e. no gradient) over the identical array ofmini-LEDs. FIG. 8A illustrates a Z-channel image of the light emittingfrom the back light unit with the standard optical film with uniformmicrostructures over the array of mini-LEDs, and FIG. 8B illustrates aZ-channel image of the light emitting from the back light unit with theoptical film 700 according to an embodiment of the invention over thearray of mini-LEDs. FIG. 9A illustrates uniformity analysis and on-axisluminance for the back light unit with the standard optical film withuniform microstructures over the array of mini-LEDs, and FIG. 9Billustrates uniformity analysis and on-axis luminance for the back lightunit with the optical film 700 according to an embodiment of theinvention over the array of mini-LEDs.

From the measurements, the back light unit with the optical film 700according to an embodiment of the invention achieved an improveduniformity of 2.0%, compared with 3.1% uniformity from the back lightunit with the standard optical film with uniform microstructures,thereby resulting in a 50% enhancement in uniformity. Luminance orbrightness also improved by over 4% when using the optical film 700according to an embodiment of the invention.

The microstructures 630 described above may be created using manytechniques known in the art. For example, in an embodiment, the shape ofthe microstructure may be cast onto a substrate using a suitable mastermold, and thermally-curing polymer or ultraviolet (UV) light curingpolymer, or the shape may be impressed into a thermoplastic substratethrough compression molding or other molding, or may be created at thesame time as the substrate using extrusion-embossing or injectionmolding. The microstructures may be produced by replicating a master.For example, an optical film may be made by replication of a mastercontaining the desired shapes as described in U.S. Pat. No. 7,190,387 B2to Rinehart et al., entitled “Systems And Methods for FabricatingOptical Microstructures Using a Cylindrical Platform and a RasteredRadiation Beam”; U.S. Pat. No. 7,867,695 B2 to Freese et al., entitled“Methods for Mastering Microstructures Through a Substrate UsingNegative Photoresist”; and/or U.S. Pat. No. 7,192,692 B2 to Wood et al.,entitled “Methods for Fabricating Microstructures by Imaging a RadiationSensitive Layer Sandwiched Between Outer Layers”, assigned to theassignee of the present invention, the disclosures of all of which areincorporated herein by reference in their entirety as if set forth fullyherein. The masters themselves may be fabricated using laser scanningtechniques described in these patents and may also be replicated toprovide microstructures using replicating techniques described in thesepatents.

In an embodiment, laser holography, known in the art, may be used tocreate a holographic pattern that creates the desired microstructures ina photosensitive material. In an embodiment, projection or contactphotolithography, such as used in semiconductor, display, circuit board,and other common technologies known in the art, may be used to exposethe microstructures into a photosensitive material. In an embodiment,laser ablation, either using a mask or using a focused and modulatedlaser beam, may be used to create the microstructures including theindicia in a material. In an embodiment, micromachining (also known asdiamond machining), known in the art, may be used to create the desiredmicrostructures from a solid material. In an embodiment, additivemanufacturing (also known as 3D printing), known in the art, may be usedto create the desired microstructure in a solid material.

FIGS. 10-15 illustrate different arrangements of microstructures 630 ofthe optical film 610 according to embodiments of the invention. Asillustrated in FIG. 10 , an optical film 1000 includes a plurality ofregions 1010 that include microstructures in the form of elongatedprisms 1030 that are sized to provide a gradient within each region1010. The dark portions between the regions 1010 do not havemicrostructures.

As illustrated in FIG. 11 , an optical film 1100 includes a plurality ofmicrostructures in the form of elongated prisms 1130 that extend acrossthe upper side of the optical film 1100. The optical film 1100 alsoinclude a plurality of regions 1110 that are sized/shaped to provide agradient within each region 1110. The dark portions between the regions1130 provide higher transmittance.

As illustrated in FIG. 12 , an optical film 1200 includes a plurality ofmicrostructures in the form of three-sided pyramids 1230 that cover theupper side of the optical film 1200. The optical film 1200 also includea plurality of regions 1210 (only a single region 1210 shown in FIG. 12) that have the three-sided pyramids 1230 sized/shaped to provide agradient within each region 1210. The dark portions outside of theregions 1210 provide higher transmittance.

As illustrated in FIG. 13 , an optical film 1300 includes a plurality ofmicrostructures in the form of cones 1330 that cover the upper side ofthe optical film 1300. The optical film 1300 also include a plurality ofregions 1310 that have the cones 1330 sized/shaped to provide a gradientwithin each region 1310. The dark portions outside of the regions 1310provide higher transmittance.

As illustrated in FIG. 14 , an optical film 1400 includes a plurality ofmicrostructures in the form of cones 1430 that cover the upper side ofthe optical film 1400. The cones 1430 of the optical film 1400 of FIG.14 are generally larger than the cones 1330 of the optical film 1300 ofFIG. 13 . The optical film 1400 also include a plurality of regions 1410that have the cones 1430 sized/shaped to provide a gradient within eachregion 1410. The dark portions outside of the regions 1410 providehigher transmittance.

As illustrated in FIG. 15 , an optical film 1500 includes a plurality ofmicrostructures 1530, 1532, 1534 in the form of a mixture of two or moretypes of lenses that cover an upper side 1502 of the optical film 1500.In an embodiment, the bottom side of the optical film 1500 (not shown)includes a plurality of microstructures in the form of elongated prismsthat extend in a first direction FD. The optical film 1500 includes aplurality of first regions 1510, a plurality of second regions 1512, anda plurality of third regions 1514.

The plurality of first regions 1510 include a plurality ofmicrostructures 1530 on the upper side 1502 of the optical film 1500 inthe form of elongated prisms that extend in a second direction SD, whichis orthogonal (perpendicular) to the first direction FD. The pluralityof first regions 1510 are arranged to be located directly above the LEDs612 in the back light unit 600, such as at locations “A” in FIG. 6 .

The plurality of second regions 1512 include a plurality ofmicrostructures 1532 on the upper side 1502 of the optical film 1500 inthe form of elongated prisms that extend in the first direction FD andare parallel to the elongated prisms on the bottom side of the opticalfilm 1500. The plurality of second regions 1512 are arranged to belocated in between the LEDs 612 in the back light unit 600, such as atlocations “B” in FIG. 6 .

The plurality of third regions 1514 include a plurality ofmicrostructures 1534 on the upper side 1502 of the optical film 1500 inthe form of a mixture of prism segments that extend in the firstdirection FD and the second direction SD. The ratio of the twoorientations of prism segments may be varied so that the plurality ofthird regions 1514 provide a gradient that transitions between themicrostructures 1530 of the first regions 1510 and the microstructures1532 of the second regions 1512.

The plurality of prisms on both sides of the optical film 1500 may haveapex angles that are substantially similar. In an embodiment, the apexangles of the prisms may be about 90°.

FIGS. 16A, 16B and 16C illustrate the effect of using the two differentorientations of parallel prisms for the first regions 1510 and thesecond regions 1512. Specifically, FIG. 16A illustrates a distribution1600 of a ˜20-degree beam emitted by an LED, as measured by agoniophotometer. FIG. 16B shows a distribution 1610 of the same beamused for FIG. 16A exiting an optical film having elongated prisms onboth sides that are parallel to each other, such as in the secondregions 1512 illustrated in FIG. 15 . As illustrated, the beam exits thefilm almost unchanged with minimum angular spreading, which may bedesirable for positions in between the LEDs (e.g., at locations “B” inFIG. 6 ). In contrast, FIG. 16C illustrates a distribution 1620 of thesame beam used for FIG. 16A exiting a film with elongated prisms on bothsides of the optical film, but with a relative orientation of 90 degreesto each other, such as in the first regions 1510 illustrated in FIG. 15. As illustrated, the beam exits the film with large angular spreading,which is desirable for the positions directly above the LEDs (e.g., atlocations “A” in FIG. 6 ). The mixture of prisms located in the thirdregions 1514 illustrated in FIG. 15 are expected to provide for angularspreading of light in between what is provided by the prisms located inthe first regions 1510 and the second regions 1512.

As illustrated in FIG. 17 , an optical film 1700 includes a plurality ofmicrostructures 1730, 1732, 1734 in the form of a mixture of two or moretypes of lenses that cover an upper side 1702 of the optical film 1700.In an embodiment, the bottom side of the optical film 1700 (not shown)includes a plurality of microstructures in the form of elongated prismsthat extend in the first direction FD. The optical film 1700 includes aplurality of first regions 1710, a plurality of second regions 1712, anda plurality of third regions 1714.

The plurality of first regions 1710 include a plurality ofmicrostructures 1730 on the upper side 1702 of the optical film 1700 inthe form of elongated prisms that extend in the second direction SD,which is orthogonal (perpendicular) to the first direction FD. Theplurality of first regions 1710 are arranged to be located directlyabove the LEDs 612 in the back light unit 600, such as at locations “A”in FIG. 6 .

The plurality of second regions 1712 include a plurality ofmicrostructures 1732 on the upper side 1702 of the optical film 1700 inthe form of elongated prisms that extend in the first direction FD andare parallel to the elongated prisms on the bottom side of the opticalfilm 1700. The plurality of second regions 1712 are arranged to belocated in between the LEDs 612 in the back light unit 600, such as atlocations “B” in FIG. 6 .

The plurality of third regions 1714 include a plurality ofmicrostructures 1734 on the upper side 1702 of the optical film 1700 inthe form of a mixture of prism segments that vary in angle relative tothe first direction FD and the second direction SD in a continuousmanner as the positions of the microstructures 1734 move away from thefirst regions 1710 so as to create a swirl-like pattern that surroundsthe plurality of microstructures 1730 in the first regions 1710, asillustrated. Such a swirl-like pattern in the third regions 1714provides a gradient that transitions between the microstructures 1730 ofthe first regions 1710 and the microstructures 1732 of the secondregions 1712, as illustrated.

The plurality of prisms on both sides of the optical film 1700 may haveapex angles that are substantially similar. In an embodiment, the apexangles of the prisms may be about 90°.

The illustrated embodiments of the optical films 1000, 1100, 1200, 1300,1400, 1500, and 1700 of FIGS. 10-15 and 17 are not intended to belimiting in any way are illustrate a wide range possible microstructureshapes and sizes that may be used for the optical film 610 of FIG. 6 .For example, for embodiments of optical films 610 that use elongatedprisms on both sides of the substrate 620, the spreading of the light inthe first regions 1510, 1710 may be varied by changing the angles at theapexes of the orthogonal prisms, with a value of about 90° providingsubstantial spreading.

The illustrated and above-described embodiments are not intended to belimiting in any way, and any such modifications to the embodimentsdescribed herein are intended to be included within the spirit and scopeof the present disclosure and protected by the claims that follow.

1-21. (canceled)
 22. An optical film for a back light unit comprising anarray of light emitting diodes, the optical film comprising: a) asubstrate; and b) a plurality of first regions of spatially modulatedmicrostructures on at least one side of the substrate, the spatiallymodulated microstructures having different sizes configured to create agradient structure within each first region, each of the plurality offirst regions being substantially circular in shape in plan-view,wherein a center of at least one of the plurality of first regions isconfigured to be positioned directly over a light emitting diodecomprising the array of light emitting diodes, the gradient structurewithin each first region being constructed and arranged to cause a firstlevel of spreading of light when positioned directly above an individuallight emitting diode and a second level of spreading of light atlocations not directly above an individual light emitting diode, thesecond level being less that the first level.
 23. The optical filmaccording to claim 22, wherein the spatially modulated microstructurescomprise a plurality of elongated prisms.
 24. The optical film accordingto claim 22, wherein the spatially modulated microstructures comprise aplurality of three-sided pyramids.
 25. The optical film according toclaim 22, wherein the spatially modulated microstructures comprise aplurality of cones.
 26. The optical film according to claim 22, whereinthe spatially modulated microstructures comprise a first plurality ofparallel prisms and a second plurality of parallel prisms.
 27. Theoptical film according to claim 26, wherein the first plurality ofparallel prisms and the second plurality of parallel prisms have apexeshaving substantially the same angles.
 28. The optical film according toclaim 27, wherein the angles are about 90°.
 29. The optical filmaccording to claim 22, wherein the plurality of first regions ofspatially modulated microstructures are configured to provide theoptical film with a lattice-type structure.
 30. The optical filmaccording to claim 22, wherein the center of at least one of theplurality of first regions is configured to be positioned directly overa mini-light emitting diode comprising the array of mini-light emittingdiodes.
 31. The optical film according to claim 22, further comprising aplurality of second regions of spatially modulated microstructures onthe at least one side of the substrate.
 32. The optical film accordingto claim 31, wherein at least one of the plurality of second regions ofspatially modulated microstructures are arranged to be located withcenters positioned in between two light emitting diodes comprising thearray of light emitting diodes.
 33. The optical film according to claim31, further comprising a plurality of third regions of spatiallymodulated microstructures on a side of the substrate that is differentfrom the at least one side of the substrate.
 34. The optical filmaccording to claim 33, wherein the plurality of third regions isconstructed and arranged to cause a third level of spreading of light,the third level being less than the first level and greater than thesecond level.
 35. The optical film according to claim 34, wherein eachof the plurality of third regions comprises a gradient comprising amixture prism segments configured to provide a gradient that transitionsbetween the microstructures of the plurality of first regions and themicrostructures of the plurality of second regions.
 36. An optical filmfor a back light unit comprising an array of light emitting diodes, theoptical film comprising: a) a substrate; and b) a plurality of firstregions of spatially modulated microstructures on at least one side ofthe substrate, the spatially modulated microstructures having differentshapes configured to create a gradient structure within each firstregion, each of the plurality of first regions being substantiallycircular in shape in plan-view, wherein a center of at least one of theplurality of first regions is configured to be positioned directly overa light emitting diode comprising the array of light emitting diodes,the gradient structure within each first region being constructed andarranged to cause a first level of spreading of light when positioneddirectly above an individual light emitting diode and a second level ofspreading of light at locations not directly above an individual lightemitting diode, the second level being less that the first level. 37.The optical film according to claim 36, wherein the spatially modulatedmicrostructures comprise a plurality of elongated prisms.
 38. Theoptical film according to claim 36, wherein the spatially modulatedmicrostructures comprise a plurality of three-sided pyramids.
 39. Theoptical film according to claim 36, wherein the spatially modulatedmicrostructures comprise a plurality of cones.
 40. The optical filmaccording to claim 36, wherein the spatially modulated microstructurescomprise a first plurality of parallel prisms and a second plurality ofparallel prisms.
 41. The optical film according to claim 40, wherein thefirst plurality of parallel prisms and the second plurality of parallelprisms have apexes having substantially the same angles.
 42. The opticalfilm according to claim 41, wherein the angles are about 90°.
 43. Theoptical film according to claim 36, wherein the plurality of firstregions of spatially modulated microstructures are configured to providethe optical film with a lattice-type structure.
 44. The optical filmaccording to claim 36, wherein the center of at least one of theplurality of first regions is configured to be positioned directly overa mini-light emitting diode comprising the array of mini-light emittingdiodes.
 45. The optical film according to claim 36, further comprising aplurality of second regions of spatially modulated microstructures onthe at least one side of the substrate.
 46. The optical film accordingto claim 45, wherein at least one of the plurality of second regions ofspatially modulated microstructures are arranged to be located withcenters positioned in between two light emitting diodes comprising thearray of light emitting diodes.
 47. The optical film according to claim45, further comprising a plurality of third regions of spatiallymodulated microstructures on a side of the substrate that is differentfrom the at least one side of the substrate.
 48. The optical filmaccording to claim 47, wherein the plurality of third regions isconstructed and arranged to cause a third level of spreading of light,the third level being less than the first level and greater than thesecond level.
 49. The optical film according to claim 48, wherein eachof the plurality of third regions comprises a gradient comprising amixture prism segments configured to provide a gradient that transitionsbetween the microstructures of the plurality of first regions and themicrostructures of the plurality of second regions.
 50. A back lightunit comprising: a) an array of light emitting diodes; and b) an opticalfilm positioned above the array of light emitting diodes, the opticalfilm comprising: i) a substrate; and ii) a plurality of first regions ofspatially modulated microstructures on at least one side of thesubstrate, the spatially modulated microstructures having differentsizes and/or shapes configured to create a gradient structure withineach first region, each of the plurality of first regions beingsubstantially circular in shape in plan-view, wherein a center of atleast one of the plurality of first regions is positioned directly overa light emitting diode comprising the array of light emitting diodes,the gradient structure within each first region being constructed andarranged to cause a first level of spreading of light when positioneddirectly above an individual light emitting diode and a second level ofspreading of light at locations not directly above an individual lightemitting diode, the second level being less that the first level. 51.The back light unit according to claim 50, wherein the array of lightemitting diodes comprises an array of mini LEDs.